Water under the home: what it does to piers, straps, and the belly

Water under a manufactured home is the cause behind most of the other problems on this site. Hidalgo County gets it two ways, a wet September on ground that does not drain and a flood year like 2018 or 2020, and the damage shows up months after the water is gone.

What is actually happening

The Texas installation rule, 10 TAC 80.21(h), describes it better than we can: “Water build-up may cause shifting or settling of the foundation, dampness in the home, damage to siding and bottom board, buckling of walls and floors, delamination of floor decking and problems with the operation of windows and doors.”

Take those one at a time. Footings lose bearing. A concrete footing sized for dry ground presses into mud, the pier on it drops, and the frame racks. Straps go slack. As the piers drop the geometry between the I-beam and the anchor head changes, and the tie-downs loosen. The belly gets wet. Standing water against the bottom board soaks the insulation, and a torn vapor retarder lets the ground keep it wet after the surface dries. The decking delaminates. Wet subfloor swells, the layers separate, and the floor goes soft.

The same thing happens under a site-built pier-and-beam house, where the victims are sills and joists rather than a bottom board; see house leveling.

Water, or something else?

Probably a plumbing leak if: the wet area is small, directly under a bathroom or kitchen, and the ground elsewhere under the home is dry.

Probably ground water if: the whole crawl is damp, there is a tide line on the piers or skirting, the ground outside is lower on one side, or a downspout empties beside the home.

Probably both if: the belly is torn and sagging. A torn belly lets a plumbing leak wet the ground and lets ground moisture wet the belly.

The two-minute check

Walk the perimeter after rain. Water standing against the skirting on one side is water standing under that side.

Open the access panel. The state’s generic standard calls for 18 inches between the ground and the floor joists. Look for a tide line on the piers, a damp smell, insulation hanging out of the belly, and daylight through the skirting where vents should be.

Count the vents. Six openings minimum, one within three feet of each corner, is the rule. Many Valley homes have skirting with two or none, and a sealed crawl holds moisture against the belly.

Why homes get this here

The uplands around Edinburg, north McAllen, and north Mission are Hidalgo sandy clay loam, well drained, and in an ordinary year the crawl under a home there dries out. South of Business 83 under Pharr, Alamo, San Juan, Donna, and Weslaco the ground is Harlingen, Mercedes, Raymondville, and Runn clay with very slow permeability, and water that reaches the crawl sits there. Harlingen clay is 60 to 75 percent clay. It does not drain; it swells.

Then there are the flood years. The McAllen normals put the wettest month in September at 4.61 inches, but June 2018 put 18.31 inches on a gauge west of Mission and 15.57 inches northeast of Weslaco, and an estimated 2,700 homes and businesses in Mission and McAllen took water. Hanna in July 2020 dropped 14.40 inches northwest of Mission and left 18 inches to four feet of water standing east of Edinburg and around Mission. A crawl that spent days under that water has soft footings and a soaked belly whether or not the home shows it yet.

Hidalgo County Drainage District No. 1, based on North Doolittle Road in Edinburg, runs the county’s drain system and has bond programs from 2018 and 2023 working through it. That is the county-scale answer. Under one home, the answer is grading, gutters, and where the downspouts go, which under the rule is the owner’s job on a used home.

What the work involves

The crew shoots the piers to find which ones dropped, then resets or rebuilds them; on ground that has proved soft, a rebuild means a larger footing so the pier presses in less next time. The belly is opened where it is torn, wet insulation comes out, and the vapor retarder is patched or replaced to the 6-mil, 12-inch-overlap standard. Vents are added where the skirting has too few. The straps are re-tensioned. And the crew looks at where the water came from, because a relevel on a lot that still floods is a relevel that gets repeated.

What it costs

Published on the pricing page.

While somebody is under there

Everything on this page is found on the same crawl. Slack straps, a soft floor, and a torn belly after a wet year are one visit, not three. See loose or rusted tie-downs and soft or bouncy floor.

What to expect on the call

Whether the home took water in 2018 or 2020, where the water stands after rain, whether there is a smell or hanging insulation at the access panel, how many vents the skirting has, and whether any doors or floors have changed. The level check is free and takes about half an hour.

We cover Edinburg, McAllen, Mission, Pharr, San Juan, Alamo, Donna, and Weslaco.